1. Field of the Invention
This invention relates to reaction chambers for high temperature processing of semiconductor wafers. More particularly, the invention relates to a compact process chamber capable of withstanding stresses associated with high temperature, low pressure processes, and having an improved service life.
2. Description of the Related Art
Reaction chambers used for semiconductor processing generally employ radiant heaters positioned on the exterior of the chamber to heat a wafer located within the chamber. The wafer is typically separated from the heaters by chamber walls, which prevent the release of the processing gases into the ambient environment. These walls are desirably made of a transparent material to allow the radiant heat to pass through the walls and heat only the wafer. This material must also be able to withstand the very high temperatures used in processing semiconductor wafers. In addition, the chamber walls are desirably made from an inert material that does not react with the processing gases at the operative temperature. Furthermore, the material used for the chamber walls desirably has high purity characteristics to minimize contamination of the chamber that impedes the wafer processing. Quartz or a similar material is popular for use in chamber walls for exhibiting the foregoing properties.
For applications in which the pressure within a quartz chamber is to be reduced much lower than the surrounding ambient pressure, cylindrical or spherical chambers have been preferred from a strength standpoint because their curved outward surfaces can aid in withstanding inwardly direct force. A dome-shaped chamber has been described in U.S. Pat. No. 5,085,887, entitled WAFER REACTOR VESSEL WINDOW WITH PRESSURE-THERMAL COMPENSATION, and in U.S. Pat. No. 5,108,792, entitled DOUBLE-DOME REACTOR FOR SEMICONDUCTOR PROCESSING, both of which have been assigned to Applied Materials, Inc. This chamber includes an upper wall having a convex outer surface and a concave inner surface. A greatly thickened peripheral flange is provided that radially confines the upper wall to cause the wall to bow outward due to thermal expansion, helping to resist the exterior ambient pressure in vacuum applications. The chamber requires a complex mechanism for clamping the thickened exterior flanges of the upper and lower chamber walls. In particular, the flange portion is secured between base plates and clamping plates and is sealed with O-rings.
A problem with double-dome chambers as described above is that such chambers typically have an abundance of metallic surfaces. As noted, the domes of the chambers are sealed to metal base plates and clamping plates through O-rings. These metal plates are necessary to provide the chamber with sufficient strength to prevent the top and bottom domes from bending. A disadvantage of this design is that the metallic surfaces of the plates and the O-rings come into contact with the processing gases and, if not adequately coated, are subject to elevated temperature and low pressure conditions. Specifically, metal found within an IR field absorbs heat, thereby requiring more power to heat the wafer, wafer holder and/or slip ring. Consequently, the metal ring is difficult to cool. Moreover, the O-rings have a tendency to deteriorate when exposed to chemicals at high temperatures. The existence of non-quartz or other non-inert surfaces in contact with the interior of the reaction chamber in close proximity to the wafer may lead to the introduction of contaminants on the wafer by reaction of the surfaces with the processing gases.
A lenticular chamber for processing of semiconductor wafers is described in pending application titled PROCESS CHAMBER WITH INNER SUPPORT, Ser. No. 08/637,616, filed Apr. 25, 1996. This chamber has thin upper and lower curved quartz walls having a convex exterior surface and a concave interior surface. These walls are welded to mate at their side edges to two quartz side rails, thus giving the chamber a generally flattened or ellipsoidal cross-section. The two side rails and an internal quartz plate provided within the chamber prevent the upper and lower walls from bending. End flanges welded to the side rails and upper and lower walls are made from translucent quartz. Thus, the lenticular chamber reduces the amount of metal exposed to the interior of the chamber, as compared to the chambers of the ""887 and ""792 patents.
Despite these advantages, there are certain disadvantages of the above-described lenticular chamber. For instance, upscaling the lenticular chamber to larger sizes is difficult. The lenticular chamber is rectangular because O-rings located at the longitudinal ends of the chamber should be kept farther away from the center of the chamber where the wafer is located. These O-rings have a tendency to heat up, and therefore, if located too close to the extreme temperatures at the center of the chamber, they will become difficult to cool and may deteriorate more easily due to thermal stresses. Moreover, a rectangular shape is desired for the lenticular chamber to more evenly distribute gas flow through the chamber. By providing a longer longitudinal distance for gas to flow over the wafer to be processed, the gas can spread out in the chamber before reaching the wafer, thereby allowing a more uniform deposition. Therefore, to upscale the design to larger sizes requires maintaining rectangular proportions in the chamber. Also, the non-symmetrical design of the chamber is not favorable to vertical gas flow, for example, when gas flow is provided through an inlet above the wafer.
Such a chamber used to process, for example, 300 mm wafers, would be extremely big and heavy, and difficult to fabricate, requiring special cranes and lifting devices. This increase in size also decreases the amount of clean room space available. Furthermore, the larger size also makes the chamber more difficult to clean.
Accordingly, a need exists for a reaction chamber for semiconductor processing that minimizes the amount of metallic and other heat-absorbing and contaminating materials in the reaction chamber. Desirably, the chamber should be compact and have sufficient strength to be used in low pressure, high temperature environments.
The above needs are satisfied by the process chambers described hereinbelow. Briefly stated, the preferred embodiments are constructed such that the process chamber has an interior surface of all-quartz or similar material. The chamber has thin upper and lower walls made from a generally transparent material, such as quartz, each preferably having a convex exterior surface and a concave interior surface. These walls are joined at their edges to a side wall or walls, preferably formed from a generally translucent material such as bubble quartz. The upper and lower walls and the side walls substantially enclose an all-quartz interior surface, except for apertures used for gas inlet and outlet and wafer transfer. An internal reinforcement extends from the inner surface of the side wall around the entire internal perimeter of the chamber to provide additional strength and support to the chamber.
As used herein, description of an all-quartz interior chamber surface refers to the enclosing surfaces of the chamber, such as the upper and lower walls and side wall, and not to the fixtures such as the slip ring and susceptor found inside the chamber. The illustrated all-quartz construction minimizes the metallic and non-quartz surfaces in the chamber, thereby making the chamber easier to cool and requiring less power consumption to heat the wafer and slip ring located inside the chamber. The use of substantially all-quartz surfaces also reduces contaminants within the chamber and alleviates fracturing of non-quartz parts due to the high temperature, low pressure environment. In one embodiment, the chamber also has a generally cylindrical, double-dome like shape so that it can be made smaller than rectangular chambers used for processing the same wafer size. This shape also provides better strength to the chamber while enabling either transverse and/or axial gas flow for a more uniform deposition.
In one aspect of the present invention, a processing chamber is provided comprising- an upper wall having a convex outer surface and a concave inner surface. A lower wall is spaced from the upper wall having a convex outer surface and a concave inner surface. Both the upper wall and the lower wall extend a length in a y dimension, a width in an x dimension and a height in a z dimension. Both these walls are curved in both x-z and y-z planes. At least one side wall having an inner surface and an outer surface connects the upper wall to the lower wall, wherein the upper wall, lower wall and the at least one side wall together substantially enclose a chamber space having all-quartz enclosing surfaces. An external reinforcement is provided on at least part of the outer surface of the at least one side wall to confine outward expansion of the chamber.
In another aspect of the present invention, the processing chamber comprises a quartz upper dome wall and a quartz lower dome wall spaced from the upper dome wall. Each dome wall has a convex outer surface and a concave inner surface. A generally cylindrical quartz side wall having an inner surface and an outer surface connects the upper and lower dome walls and defines a chamber space therebetween. A retainer surrounds at least a portion of the outer surface of the side wall to confine outward expansion of the chamber. The chamber space is substantially enclosed only by the inner surfaces of the dome wall and the inner surface of the side wall.
In another aspect of the present invention, a processing chamber having an upstream end and a downstream end and lateral sides extending therebetween is provided. The chamber comprises an upper wall and a lower wall spaced from the upper wall, each wall being outwardly curved in both a lateral and a longitudinal direction. A plurality of side walls connects the upper and lower walls. The plurality of side walls includes an inlet flange connecting the upper and lower walls at the upstream end of the chamber, an outlet flange connecting the upper and lower walls at the downstream end of the chamber, and side rails connecting the upper and lower walls at the lateral sides of the chamber and connecting the inlet and outlet flanges between the upstream and downstream ends of the chamber. An external reinforcement is provided along at least a portion of the plurality of side walls to confine outward expansion of the chamber. The chamber has a substantially all-quartz interior surface defined by the upper and lower walls and the plurality of side walls.
In another aspect of the present invention, a chamber for processing semiconductor wafers and the like is provided. The chamber comprises outwardly convex upper and lower walls each having outer and inner surfaces and being curved in a lateral and a longitudinal direction. At least one side wall connects the upper and lower walls, the at least one side wall having inner surfaces that are substantially flush with the inner surfaces of the upper and lower walls at the connection between the edges of the at least one side wall and the upper and lower walls. The upper and lower walls and the at least one side wall enclose a chamber space having a substantially continuous inner surface formed of a nonreactive substantially light-transmissive material.
In another aspect of the present invention, the processing chamber comprises an upper wall and a lower wall that are both curved in x-z and y-z planes. At least one side wall connects the upper and lower walls such that the at least one side wall and the upper and lower walls confine a chamber space. A reinforcement extends along the entire interior perimeter of the chamber space to prevent outward expansion of the chamber.
In another aspect of the present invention, a processing chamber is provided having an upstream end and a downstream end defining a longitudinal axis of the chamber, and a lateral axis perpendicular to the longitudinal axis. The chamber comprises outwardly curved upper and lower walls, each wall being substantially rectangular when viewed from above. Each wall is outwardly curved along both its longitudinal and lateral axes. Side walls connect the upper and lower walls.
In another aspect of the present invention, a processing chamber having an upstream end and a downstream end and lateral sides extending therebetween is provided. An upper wall extends a length in a y dimension between the upstream and downstream ends, a width in an x dimension between the lateral sides, and a height in a z dimension. A lower wall also extends a length in the y dimension, a width in the x dimension, and a height in the z dimension. The upper wall and the lower wall each has a substantially convex outer surface and is formed of a substantially non-reactive light transmissive material. At least one side wall connects the upper wall to the lower wall to define a chamber space therebetween. The at least one side wall thereby defines an outer periphery of the chamber space and is formed of a substantially non-reactive light transmissive material. An external reinforcement extends substantially entirely around the outer periphery of the chamber space to confine outward expansion of the chamber.